How do I make steel in cycles using 2.5 as the IOR?
The FRESNEL node connected to a the FACTOR input of a MIX node which has for example a DIFFUSE and GLOSSY input will change the reflections depending on the angle that light strikes it.

The FRESNEL node has a panel for the IOR

http://www.chocofur.com/6-shadersamptextures.html